The field of the disclosure relates generally but not exclusively to wireless tag readers, such as Radio Frequency Identification (RFID) tag readers, and, more particularly, to methods and apparatus for ranging a wireless tag relative to a tag reader.
Wireless transponders or tags, such as RFID tags, are used in combination with RFID interrogators to identify an object or objects. Typically, when these tags are excited, they produce or reflect a magnetic or electric field at some frequency, which may be modulated with an identifying code or other useful information.
RFID tags may either be active or passive. Active tags have a self-contained power supply. Passive tags require external excitation in order to be read within the read volume of an interrogator or reader. In passive tag systems, the interrogator or reader typically contains a transmitting antenna for sending an exciting frequency signal to the passive tag. The transmitting antenna is often positioned adjacent to an antenna for receiving a modulated signal (magnetic or electromagnetic) produced by the excited tag. This modulated signal may identify the tag and, consequently, the object associated with the tag.
Current implementations of RFID readers return only the digital data associated with the tag, rather than information regarding the distance to the tag. The present inventors have therefore recognized a need for systems and methods for effectively determining a measured distance between an RFID reader and an RFID tag when interrogated by the RFID reader.